|Abstract: ||A temperature insensitive (athermal) channeled spectropolarimeter (CSP)
is described. The athermal CSP includes a crystal retarder formed of a
biaxial crystal. The crystal retarder has three crystal axes, wherein
each axis has its own distinct index of refraction. The axes are oriented
in a particular manner, causing an amplitude modulating carrier frequency
induced by the crystal retarder to be thermally invariant. Accordingly, a
calibration beam technique can be used over a relatively wide range of
ambient temperatures, with a common calibration data set.